With a great increase in the amount of data to be processed in the information telecommunication field, there is a demand for an increase in signal transmission speed within a device and between devices. In recent years, in order to cope with such high-speed transmission, a differential transmission system has been used.
For example, a system using a cable with a connector such as a quad small form-factor pluggable (QSFP) is adopted for transmission within the device and between devices, and for example, a direct attach cable (DAC) is frequently used. However, since the transmission distance of the DAC is limited to about 3 m, a longer transmission distance is required. In addition, for example, in such high-speed transmission exceeding 25 Gbit/s, loss in a transmission line becomes a problem. For this reason, application of an active copper cable (ACC) in which an equalization element for compensating for loss occurring in a transmission line is mounted in a connector such as QSFP as a transmission cable which replaces the DAC has been studied. As a board of the connector used for this cable, a multilayer board where two or more types of resin boards having different thicknesses are laminated is frequently used.
The equalization element of the ACC is mounted on one side of the multilayer board in consideration of assembly cost and reliability after mounting the element. On the other hand, in general, signal input/output pins of the connector are provided on both front and back surfaces of the multilayer board from the viewpoint of high density. Therefore, in the multilayer board for the connector of the ACC, for example, it is required that a pin on the surface on which an equalization element is not mounted can be electrically connected to the equalization element by providing a through-hole. For example, Patent Document 1 discloses a configuration example where a land of a first wire line layer and a land of an n-th wire line layer are connected by a via-hole provided inside a multilayer printed wiring board.